Electronic Device Including a Transistor and a Variable Resistor

ABSTRACT

In an aspect, a circuit can include drain and source terminals; a HEMT having a drain and a source, wherein the drain is coupled to the drain terminal; and a variable resistor having a first electrode and a second electrode. The first electrode can be coupled to the source of the HEMT, and the second electrode can be coupled to the source terminal. In another aspect, an electronic device can include a source terminal; a heterojunction between a channel layer and a barrier layer; a source electrode of a HEMT overlying the channel layer; a first resistor electrode overlying the channel layer and spaced apart from the source electrode, wherein the first resistor electrode is coupled to the source terminal; and a variable resistor, wherein from a top view, the variable resistor is disposed along the heterojunction between the source electrode and the first resistor electrode.

FIELD OF THE DISCLOSURE

The present disclosure relates to electronic devices, and moreparticularly to, electronic devices that include transistors andvariable resistors.

RELATED ART

When transistors are turned on and off, transistors can experiencetransient conditions that are not present when the transistors are onand off for an extended period (at steady state). Silicon-basedtransistors can withstand some transient conditions due to the presenceof diodes as pn junctions within the active region. Such pn junctionscan occur at a drain-body interface and a source-body interface. Unlikesilicon-based transistors, high electron mobility transistors do nothave pn junctions within the active region. Accordingly, a transient,over-voltage, or over-current condition for high electron mobilitytransistors may use another physical design to address such condition.Further improvements to address transient, over-voltage, or over-currentconditions are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited in theaccompanying figures.

FIG. 1 includes a depiction of a schematic diagram of a circuit inaccordance with an embodiment.

FIG. 2 includes a depiction of a schematic diagram of a circuit inaccordance with another embodiment.

FIG. 3 includes an illustration of cross-sectional views of portions ofa workpiece that include a high electron mobility transistor and avariable resistor.

FIG. 4 includes plots of resistance as a function of voltage fordifferent corresponding distances for the variable resistor.

FIG. 5 includes an illustration of a top view of a layout for anelectronic device that includes the transistor and variable resistor inFIG. 3 in accordance with an embodiment.

FIG. 6 includes an illustration of a top view of a layout for anelectronic device that includes the transistor and variable resistor inFIG. 3 in accordance with another embodiment.

FIG. 7 includes an illustration of a top view of a layout for thevariable resistor in accordance with an embodiment.

FIG. 8 includes an illustration of a top view of a layout for thevariable resistor in accordance with another embodiment.

FIG. 9 includes an illustration of a portion of a workpiece thatincludes the variable resistor and a field electrode.

FIG. 10 includes plots of resistance as a function of voltage fordifferent corresponding distances for the variable resistor and thefield electrode.

FIG. 11 includes a depiction of a schematic diagram of a circuit furtherincluding an inductor in accordance with an embodiment.

FIG. 12 includes an illustration of a hybrid cross-sectional andperspective view of portions of a workpiece that include the highelectron mobility transistor, the inductor and the variable resistor.

FIG. 13 includes an illustration of a top view of a layout for thevariable resistor and the inductor in accordance with an embodiment.

FIG. 14 includes an illustration of a top view of a layout for thevariable resistor and the inductor in accordance with anotherembodiment.

FIG. 15 includes plots of operating parameters during short-circuitsimulation without considering self-heating effects.

FIG. 16 includes plots of operating parameters during short-circuitsimulation when considering self-heating effects.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of embodiments of the invention.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings. However, other embodiments can be usedbased on the teachings as disclosed in this application.

Group numbers corresponding to columns within the Periodic Table ofElements based on the IUPAC Periodic Table of Elements, version datedNov. 28, 2016.

The term “compound semiconductor” is intended to mean a semiconductormaterial that includes at least two different elements. Examples includeSiC, SiGe, GaN, InP, Al_(w)Ga_((1-w))N where 0≤w≤1, CdTe, and the like.A III-V semiconductor material is intended to mean a semiconductormaterial that includes at least one trivalent metal element and at leastone Group 15 element. A III-N semiconductor material is intended to meana semiconductor material that includes at least one trivalent metalelement and nitrogen. A Group 13-Group 15 semiconductor material isintended to mean a semiconductor material that includes at least oneGroup 13 element and at least one Group 15 element.

The term “high voltage,” with reference to a layer, a structure, or adevice, means that such layer, structure, or device can withstand atleast 50 V difference across such layer, structure, or device (e.g.,between a source and a drain of a transistor when in an off-state)without exhibiting dielectric breakdown, avalanche breakdown, or thelike.

The terms “normal operation” and “normal operating state” refer toconditions under which an electronic component or device is designed tooperate. The conditions may be obtained from a data sheet or otherinformation regarding voltages, currents, capacitances, resistances, orother electrical parameters. Thus, normal operation does not includeoperating an electrical component or device well beyond its designlimits.

For clarity of the drawings, certain regions of device structures, suchas doped regions or dielectric regions, may be illustrated as havinggenerally straight line edges and precise angular corners. However,those skilled in the art understand that, due to the diffusion andactivation of dopants or formation of layers, the edges of such regionsgenerally may not be straight lines and that the corners may not beprecise angles.

The terms “on,” “overlying,” and “over” may be used to indicate that twoor more elements are in direct physical contact with each other.However, “over” may also mean that two or more elements are not indirect contact with each other. For example, “over” may mean that oneelement is above another element but the elements do not contact eachother and may have another element or elements in between the twoelements.

The terms “comprises,” “comprising,” “includes,” “including,” “has,”“having” or any other variation thereof, are intended to cover anon-exclusive inclusion. For example, a method, article, or apparatusthat comprises a list of features is not necessarily limited only tothose features but may include other features not expressly listed orinherent to such method, article, or apparatus. Further, unlessexpressly stated to the contrary, “or” refers to an inclusive- or andnot to an exclusive-or. For example, a condition A or B is satisfied byany one of the following: A is true (or present) and B is false (or notpresent), A is false (or not present) and B is true (or present), andboth A and B are true (or present).

Also, the use of “a” or “an” is employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one, at least one, or the singular as alsoincluding the plural, or vice versa, unless it is clear that it is meantotherwise. For example, when a single item is described herein, morethan one item may be used in place of a single item. Similarly, wheremore than one item is described herein, a single item may be substitutedfor that more than one item.

The use of the word “about”, “approximately”, or “substantially” isintended to mean that a value of a parameter is close to a stated valueor position. However, minor differences may prevent the values orpositions from being exactly as stated. Thus, differences of up to tenpercent (10%) (and up to twenty percent (20%) for semiconductor dopingconcentrations) for the value are reasonable differences from the idealgoal of exactly as described.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and may be found in textbooks andother sources within the semiconductor and electronic arts.

A circuit can include a high electron mobility transistor (HEMT) and avariable resistor. The variable resistor can help to significantlyincrease the likelihood that the HEMT can survive a short circuit eventof limited time duration as compared to the HEMT without the variableresistor. The variable resistance within the variable resistor can allowfor good on-state current (R_(DSON)) because the resistance isrelatively lower when the HEMT is on and at steady state. During a shortcircuit event, the voltage across the variable resistor increases, andthus, the resistance increased. The increased resistance of the variableresistor during a current surge enhances the voltage at the HEMT sourceand reduces the potential difference between gate and source potential,thus pinching-off the two dimensional electron gas (2 DEG). This effectis described in more detail later in this specification. The increasedresistance helps to limit the current through the HEMT during a shortcircuit event and increases the likelihood that the HEMT survives theshort circuit event. In an electronic device, the variable resistor canbe implemented without substantially increasing the area occupied by thecircuit, as compared to the circuit with only the HEMT. In anembodiment, no additional masking or processing steps are required toform the variable resistor. If needed or desired, a field electrode oran inductor can be used in conjunction with the variable resistor tofurther increase the rate at which resistance changes as the voltageacross the variable resistor is farther away from 0 V.

In as aspect, a circuit can include a drain terminal and a sourceterminal; a high electron mobility transistor having a drain and asource, wherein the drain is coupled to the drain terminal of thecircuit; and a variable resistor having a first electrode and a secondelectrode. The first electrode can be coupled to the source of the highelectron mobility transistor, the second electrode can be coupled to thesource terminal of the circuit, and the variable resistor can have aresistance that varies as a function of at least a voltage across thevariable resistor.

In another aspect, an electronic device can include a source terminal; aheterojunction between a channel layer and a barrier layer; a sourceelectrode of a high electron mobility transistor overlying the channeland barrier layers; a first resistor electrode overlying the channel andbarrier layers and spaced apart from the source electrode, wherein thefirst resistor electrode is coupled to the source terminal; and avariable resistor, wherein from a top view, the variable resistor isdisposed along the heterojunction between the source electrode and thefirst resistor electrode.

FIG. 1 includes a depiction of a schematic of a circuit 100 thatincludes a high electron mobility transistor (HEMT) 122 and a variableresistor 126. A drain terminal 102 for the circuit 100 is coupled to adrain of the HEMT 122, a control terminal 104 is coupled to a gate ofthe HEMT 122, an electrode of the variable resistor 126 is coupled tothe source of the HEMT 122, and the other electrode of the variableresistor 126 is coupled to a source terminal 106 of the circuit 100.

Unlike many resistors that have substantially constant resistance, theresistance of a variable resistor 126 varies as a function of at leastthe voltage across a variable resistor. The resistance of the variableresistor 126 may be selected based at least in part on the normaloperating parameters of the HEMT 122, such as the nominal voltage of thecircuit 100, current that flows through the circuit when the HEMT 122 ison, another suitable parameter, or the like. In an embodiment, at a 0 Vdifference across the variable resistor 126, the resistance of thevariable resistor is in a range from 0.2 ohm to 200 ohms, depending onthe dimensions of the variable resistor 126. At −10 V or at +10 V, theresistance of the variable resistor may be in a range from 500 ohms to9000 ohms, possibly higher, depending on the dimensions of the variableresistor 126.

The HEMT 122 can be an enhancement-mode HEMT, as illustrated in FIG. 1.In another embodiment as illustrated in FIG. 2, a depletion-mode HEMT222 may be used in place of the enhancement-mode HEMT. For simplicity, aphysical design of the circuit 100 addresses the HEMT 122. After readingthis specification, skilled artisans will understand how to modify thephysical structure for the HEMT 222 in FIG. 2.

FIG. 3 includes a cross-sectional view of a portion of a workpiece 300that includes a physical design for the HEMT 122 and variable resistor126 in FIG. 1. The variable resistor 126 can be on the same workpiece ora different workpiece. If needed or desired, the variable resistor 126may be a discrete component. The description below is based on the HEMT122 and the variable resistor 126 being on the same workpiece 300. In afinished electronic device, the variable resistor 126 may be located onthe same die as the HEMT 122 or may be on a different die.

The workpiece 300 includes a substrate 320 and a dielectric layer 330.The substrate 320 includes a base material 322, a buffer layer 324, achannel layer 326, and a barrier layer 328. The base material 322 caninclude silicon, sapphire (monocrystalline Al₂O₃), silicon carbide(SiC), aluminum nitride (AlN), gallium oxide (Ga₂O₃), spinel (MgAl₂O₄),another suitable substantially monocrystalline material, or the like.The buffer layer 324 can form formed over the base material 322 to helpwith supporting a high voltage and to provide a template for the channellayer 326. The buffer layer 324 can have a thickness in a range fromapproximately 1 micron to 10 microns.

The channel layer 326 is formed over the buffer layer 324 and the basematerial 322. The channel layer 326 can include a monocrystallinecompound semiconductor material. In an embodiment, the channel layer 326can include a Group 13-N material, such as Al_(y)Ga_((1-y))N, wherein0≤y≤0.1. In a particular embodiment, the channel layer 326 includes GaN(in the prior formula, y=0). The channel layer 326 may have a thicknessin a range from 10 nm to 2000 nm. The barrier layer 328 can includeAl_(z)Ga_((1-z))N, wherein 0.02≤z≤1. In a particular embodiment, thebarrier layer 328 includes AlN (in the prior formula, z=1). The barrierlayer 328 can have a thickness in a range from 2 nm to 40 nm. The layers326 and 328 can be formed using an epitaxial growth technique, and thusthe layers 326 and 328, and at least a portion of the buffer layer 324can be monocrystalline.

The dielectric layer 330 can include an oxide, nitride, or an oxynitrideand be formed over the barrier layer 328. In an embodiment, thedielectric layer 330 can include silicon nitride and have a thickness ina range from 0 nm to 2000 nm. In an alternative embodiment, thedielectric layer 330 can include a gate dielectric film, an intermediatefilm and a capping film. The gate dielectric film can include a silicondioxide, a silicon nitride, an aluminum oxide, a zirconium oxide, ahafnium oxide, a niobium oxide, another suitable gate dielectricmaterial, or any combination thereof and have a thickness in a rangefrom 0 nm to 100 nm. The intermediate film can act as an etch-stop filmwhen etching the capping film. In an embodiment, the intermediate filmcan include AlN and have a thickness in a range from 0 nm to 20 nm. Thecapping film can protect the gate dielectric film. In an embodiment, thecapping film can include oxide, nitride, or an oxynitride and have athickness in a range from 0 nm to 5000 nm.

The gate of the HEMT 122 can include a p-type semiconductor layer 342.In an embodiment, the p-type semiconductor layer 342 can includeAl_(x)Ga_((1-x))N, wherein 0≤x≤1. The p-type dopant in the semiconductorlayer 342 can include Mg, C, or the like. In an embodiment, the dopantconcentration in the p-type semiconductor layer 342 can be in a rangefrom 1×10¹⁸ atoms/cm³ to 1×10²¹ atoms/cm³. The p-type semiconductorlayer 342 can have a thickness in a range from 0 nm to 200 nm. The gatecan further include a gate electrode 344. The HEMT 122 further includesa drain electrode 362 and a source electrode 366.

The variable resistor 126 includes resistor electrodes 372 and 376. Thevariable resistor has a corresponding distance 386 between the resistorelectrodes 372 and 376. The distance 386 can be in a range fromapproximately 0.5 microns to 50 microns. The particular value for thedistance 386 can depend on the particular application, voltage rating ofthe HEMT 122, another suitable parameter, or any combination thereof. Inan embodiment in which the HEMT 122 and variable resistor 126 are on thesame die, the source electrode 366 and the resistor electrode 372 may bedifferent parts of the same monolithic piece of a conductive layer.

The electrodes for the HEMT 122 and resistor electrodes of the variableresistor 126 may be formed from the same or different conductive layers.In an embodiment, part of the dielectric layer 330 may be deposited andpatterned for a gate opening where the p-type semiconductor layer 342 isto be formed for the gate of the HEMT 122.

After forming the p-type semiconductor layer 342 within the gateopening, a remaining portion of the dielectric layer 330 can be formed.The dielectric layer 330 can be patterned to define openings for theelectrodes 362, 366, 372 and 376. A conductive layer can be depositedwith the openings and patterned to form the electrodes 362, 366, 372,and 376. The conductive layer can include one or more films includingTi, TiN, Al, Cu, Pd, Pt, W, Au, Ni, or a stack or any combinationthereof. In another embodiment, the conductive layer is typically atleast 70 wt % aluminum, a noble metal, or an alloy of any of theforegoing. In the electrodes 362, 366, 372 and 376, the film closest tothe barrier layer 328 may be selected for a desired work function.

The conductive layer for the gate electrode 344 can include any of thematerials as previously described with respect to the electrodes 362,366, 372 and 376. In the gate electrode 344, the film closest to thep-type semiconductor layer 342 may be selected for a desired workfunction. Thus, the gate electrode 344 may be formed at a different timeand have a different composition as compared to the electrodes 362, 366,372 and 376. In another embodiment, the gate electrode 344 may be formedusing the same process sequence in forming the electrodes 362, 366, 372and 376 or have the same composition as the electrodes 362, 366, 372 and376.

One or more additional interconnector levels and a passivation layer(not illustrated) can be formed to form a substantially completeddevice. In a finished device, the drain electrode 362 is coupled to thedrain terminal 102, the gate electrode 344 is coupled to the controlterminal 104, the electrodes 366 and 372 can be electrically connectedto each other, and the resistor electrode 376 is coupled to the sourceterminal 106. A two-dimension electron gas 329 is formed at theheterojunction between the channel layer 326 and the barrier layer 328,except under the p-type semiconductor layer 342.

FIG. 4 includes a plot of resistance as a function of voltage betweenthe electrodes 372 and 376 for the variable resistor 126. Differentcurves correspond to different distances 386. For conventionalresistors, the resistance is substantially constant over a significantvoltage range, such as from −10 V to +10 V. As seen in FIG. 4, theresistance across the variable resistor 126 increases as the voltagedeviates from 0 V. In the embodiment, the resistance increasesexponentially with a linear change in voltage across the electrodes 372and 376. In another embodiment, the resistance may increase linearlywith a linear change in voltage across the electrode 372 and 376. Aswill be addressed later in this specification, the increased resistancecan help in reducing the likelihood of failure of the HEMT 122 duringtransient short circuit behavior.

FIGS. 5 and 6 include illustrations of top views of exemplary layouts ofthe electronic device that includes the circuit 100. The drain, gate,and source electrodes 362, 344, and 366 are illustrated near the middleof the figures. Referring to FIG. 5, a drain bond pad 562 iselectrically connected to the drain electrodes 362, gate bond pads 544are electrically connected to the gate electrodes 344, and a source bondpad 566 is electrically connected to the electrodes 366 of the variableresistor 126 that occupies area 542. The bond pads can be formed usingthe any of the materials and techniques described with respect to theconductive layers used for the electrodes 344, 362, 366, 376, and 372.In another embodiment, the bond pads 562 and 566 can be replaced byconductive plates. Referring to FIG. 6, a drain plate 662 iselectrically connected to the drain electrodes 362 via contacts 632, thegate bond pads 544 are electrically connected to the gate electrodes344, and a source plate 666 is electrically connected to the electrodesof the variable resistor that occupies area 542. The drain and sourceplates 662 and 666 can be plated onto the workpiece or may be attachedas a conductive foil. A conductive material for the drain and sourceplates 662 and 666 can include Cu, Ni, Au, or the like. Intermediatemetallization, such as Ti, TiN, TiW, W, or the like may be formed beforeplating if needed or desired.

FIGS. 7 and 8 include illustrations of top views of exemplary layoutsfor the variable resistor 126. The layout 726 includes the resistorelectrodes 372 and 376 that lie within the area 542 (in FIGS. 5 and 6).In the embodiment illustrated, the resistor electrodes 372 and 376 havean inter-digitated pattern. In an embodiment as illustrated, theresistor electrode 372 includes projections extending toward theresistor electrode 376, and the resistor electrode 376 includesprojections extending toward the resistor electrode 372. The resistorelectrodes 372 and 376 do not have to be arranged in an inter-digitatedpattern, and another pattern may be used. The layout 826 includes theresistor electrodes 372 and 376 that lies within the area 542 (in FIGS.5 and 6). As compared to FIG. 7, the layout in FIG. 8 is morecomplicated.

After reading this specification, skilled artisans will appreciate thatthe layouts in FIGS. 5 to 8 are merely exemplary. Many other layouts canbe used without deviating from the concepts as described herein.Accordingly, the layouts in FIGS. 5 to 8 do not limit the scope of thepresent invention that is defined in the appended claims.

In another embodiment, a field electrode 974 may be used in conjunctionwith the physical structure that is at least part of the variableresistor 126, as illustrated in FIG. 9. The field electrode 974 can helpto further increase the resistance as a function of voltage. Asillustrated, the field electrode 974 is electrically connected to theresistor electrode 376. The field electrode 974 extends over theunderlying layers by a corresponding distance 984. The distance 984 canbe in a range from 0.2 micron to 30 microns. When expressed as afraction of the distance 386 (FIG. 3), the distance 984 can be in arange from 5% to 90% of the distance 386. In an embodiment, the distance984 can be in a range from 11% to 50% of the distance 386. The fieldelectrode 974 may be formed using the same materials and during the sameprocess sequence as the gate electrode 344. Thus, the field electrode974 can be incorporated into a process flow without adding an additionalmasking or other processing operations. FIG. 10 includes plots ofresistance as a function of voltage for a variety of distances 386(noted as D386 in FIG. 10) and 984 (noted as D984 in FIG. 10). Theeffect of the field electrode 974 on the resistance is greater for therelatively smaller distances 386 as compared to the relatively largerdistances 386.

FIG. 11 includes a depiction of a schematic diagram of a circuit 1100that is similar to the circuit 100 except that circuit 1100 includes aninductor 1125. One electrode of the inductor 1125 is coupled to thesource of the HEMT 122, and the other electrode of the inductor 1125 iscoupled to one of the resistor electrodes of the variable resistor 126.The inductor 1125 may help current to continue to flow through thevariable resistor 126 after the HEMT 122 is turned off. The inductanceof the inductor 1125 may be selected based at least in part on thenormal operating parameters of the HEMT 122, such as the nominal voltageof the circuit 1100, current that flows through the circuit when theHEMT 122 is on, another suitable parameter, or the like. In anembodiment, the inductance can be in a range from 0.01 nH to 100 nH, andin a particular embodiment, the inductance can be in a range from 0.2 nHto 2 nH.

FIG. 12 includes an illustration of a workpiece that includes a physicalstructure of the inductor 1125. The portions corresponding to the HEMT122 and variable resistor 126 are described with respect to FIG. 3. Theinductor 1125 includes an inductor electrode 1266 coupled to the sourceelectrode 366 of the HEMT 122. The inductor 1125 also includes anotherinductor electrode 1272 coupled to the resistor electrode 372 of thevariable resistor 126. The inductor 1125 further includes windings 1226that can be formed using the interconnect level used in forming theelectrodes 344, 362, 366, 372, and 376. In another embodiment, thewindings 1226 can be formed using additional interconnect levels. Adielectric material 1230 can be used in the core of the inductor 1125.The dielectric material 1230 can include any of the materials aspreviously described with respect to the dielectric material 330.

FIGS. 13 and 14 include illustrations of top views of exemplary layoutsfor the variable resistor 126 and the inductor 1125. The variableresistor 126 and the inductor 1125 may be formed at the sameinterconnect level. The variable resistor 126 and the inductor 1125 canbe electrically connected to each other using an interconnect formed ata different interconnect level. After reading this specification,skilled artisans will appreciate that the layouts in FIGS. 13 and 14 aremerely exemplary. Many other layouts can be used without deviating fromthe concepts as described herein. Accordingly, the layouts in FIGS. 13and 14 do not limit the scope of the present invention that is definedin the appended claims.

Short circuit simulations can be performed using the circuit 100 in FIG.1 and a conventional circuit that does not have a variable resistor 126(“VR” in FIGS. 15 and 16), where the source electrode of the HEMT 122 isdirectly connected to the source terminal. Thus, “HEMT+VR” correspondsto circuit 100 in FIG. 1, and “HEMT only” refers to the HEMT 122 withoutany variable resistor. FIGS. 15 and 16 include the simulation circuit.For the simulation, Vbus is 400 V, and the voltage between the gate andsource terminals 104 and 106 is −3 V when the circuit is off, and +5 Vwhen the circuit is on. The circuits are pulsed on for a time period ofa microsecond.

FIG. 15 includes plots of operating parameters without consideringself-heating effects. The resistance between the gate driver and thegate electrode of the HEMT is 50 ohms (Rg=50 ohms). At t=1e-06 s, theHEMT only circuit is turned on, and the drain current (Id) increases toover 40 A in a few tenths of a microsecond and remains at a relativelyhigh current at least until t=2e-06 s. In circuit 100, the variableresistor 126 allows the Id to be much lower. In about a tenth of amicrosecond, Id is in a range from 12 A to 14 A, substantially lowerthan the Id of the HEMT only circuit. Thus, the variable resistor 126helps to limit the current flow through the HEMT 122 during a shortcircuit event.

FIG. 16 includes plots of operation parameters when consideringself-heating effects. The resistance between the gate driver and thegate electrode of the HEMT is 2.5 ohms (Rg=2.5 ohms). At t=1e-06, thetransistor in the HEMT only simulation is turned on, and Id increases toover 40 A in less than a tenth of a microsecond. The maximum temperature(Tmax) within the HEMT increases very quickly. As Tmax continues torise, Id peaks and falls quickly. Thus, the HEMT no longer operatesproperly and fails. Unlike the HEMT only circuit, the circuit 100 has anId that reaches approximately 14 A and slowly declines to approximately10 A when t=2e-06 s. Tmax for the HEMT 122 in the circuit 100 increasesmuch more slowly. Tmax for the variable resistor 126 remains near roomtemperature (approximately 295 K). Thus, circuit 100 passes the test.

The use of a variable resistor in circuit that includes a HEMT cansignificantly increase the likelihood that the HEMT can survive a shortcircuit event of limited time duration as compared to the HEMT withoutthe variable resistor. The variable resistance within the variableresistor 126 allows for good on-state current because the resistance isrelatively lower. During a short circuit event, the voltage across thevariable resistor increases, and thus, the resistance increase. Theincreased resistance of VR during a current surge enhances the voltageat the HEMT source and reduces the potential difference between gate andsource potential, thus pinching-off the 2 DEG. This effect isillustrated in FIG. 15 by the V_(VR) dashed line (which is the voltagedrop in VR and, at the same time, the voltage at the HEMT source whenthe source terminal 106 is at 0 V. The increased resistance helps tolimit the current through the HEMT 122 during a short circuit event andincreases the likelihood that the HEMT 122 survives the short circuitevent.

The variable resistor 126 can be implemented into a physical structurewithout substantially increasing the area occupied by the circuit 100,as compared to the circuit with only the HEMT 122. No additional maskingor processing steps are required to form the variable resistor 126. Ifneeded or desired, a field electrode or an inductor can be used inconjunction with the variable resistor 126 to further increase the rateat which resistance changes as the voltage across the variable resistor126 is farther away from 0 V.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described below. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Embodiments may be in accordance with any one or moreof the embodiments as listed below.

Embodiment 1

An electronic device can include a source terminal; a heterojunctionbetween a channel layer and a barrier layer; a source electrode of ahigh electron mobility transistor overlying the channel and barrierlayers; a first resistor electrode overlying the channel and barrierlayers and spaced apart from the source electrode, wherein the firstresistor electrode is coupled to the source terminal; and a variableresistor, wherein from a top view, a variable resistor is disposed alongthe heterojunction between the source electrode and the first resistorelectrode.

Embodiment 2

The electronic device of Embodiment 1, wherein a variable resistor has acorresponding distance in a range from approximately 0.5 microns to 50microns.

Embodiment 3

The electronic device of Embodiment 1, wherein the high electronmobility transistor and the variable resistor are on a same die.

Embodiment 4

The electronic device of Embodiment 1, wherein a variable resistor has aresistance that increases exponentially with a linear increase involtage across a variable resistor.

Embodiment 5

The electronic device of Embodiment 1, further including a secondresistor electrode that is coupled to the source electrode.

Embodiment 6

The electronic device of Embodiment 5, further including an inductorthat includes a first electrode coupled to the source electrode and asecond electrode coupled to the second resistor electrode.

Embodiment 7

The electronic device of Embodiment 6, wherein the inductor is a planarinductor.

Embodiment 8

The electronic device of Embodiment 6, further including an interconnectthat electrically connects the inductor and the second resistorelectrode to each other.

Embodiment 9

The electronic device of Embodiment 5, wherein the first resistorelectrode includes first projections extending toward the secondresistor electrode, and the second resistor electrode includes secondprojections extending toward the first resistor electrode.

Embodiment 10

The electronic device of Embodiment 1, further including a fieldelectrode that overlies a portion of a variable resistor.

Embodiment 11

The electronic device of Embodiment 10, wherein the field electrode iselectrically connected to the first resistor electrode.

Embodiment 12

The electronic device of Embodiment 10, wherein a variable resistor hasa corresponding distance, and the field electrode extends over avariable resistor in a range from 5% to 50% of the correspondingdistance.

Embodiment 13

The electronic device of Embodiment 1, further including a gateelectrode of the high electron mobility transistor and a drain electrodeof the high electron mobility transistor.

Embodiment 14

The electronic device of Embodiment 12, further including a source bondpad electrically connected to the first resistor electrode, and a drainbond pad electrically connecting to the drain electrode of the highelectron mobility transistor.

Embodiment 15

The electronic device of Embodiment 12, further including a source plateoverlying and electrically connected to the first resistor electrode,and a drain plate overlying and electrically connected to the drainelectrode of the high electron mobility transistor.

Embodiment 16

The electronic device of Embodiment 15, wherein the source plateoverlies a portion of the drain electrode of the high electron mobilitytransistor, and the drain plate overlies a portion of source electrodeof the high electron mobility transistor

Embodiment 17

A process of forming an electronic device can include providing asubstrate including a channel layer and a barrier layer, wherein aheterojunction lies between the channel and barrier layers; forming asource electrode of a high electron mobility transistor overlying thechannel and barrier layers; and forming a resistor electrode overlyingthe channel and barrier layers and spaced apart from the sourceelectrode. From a top view, a variable resistor can be disposed alongthe heterojunction between the source electrode and a variable resistorelectrode.

Embodiment 18

A circuit can include a drain terminal and a source terminal; a highelectron mobility transistor having a drain and a source, wherein thedrain is coupled to the drain terminal of the circuit; and a variableresistor having a first electrode and a second electrode. The firstelectrode can be coupled to the source of the high electron mobilitytransistor, the second electrode can be coupled to the source terminalof the circuit, and the variable resistor can have a resistance thatvaries as a function of at least a voltage across a variable resistor.

Embodiment 19

The circuit of Embodiment 18, further including an inductor having afirst electrode and a second electrode, wherein the first electrode ofthe inductor is coupled to the source of the high electron mobilitytransistor, and the second electrode of the inductor is electricallyconnected to the first electrode of the variable resistor.

Embodiment 20

The circuit of Embodiment 18, further including a control terminalcoupled to a gate of the high electron mobility transistor.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Separate embodiments may also beprovided in combination in a single embodiment, and conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range. Many other embodiments may be apparent toskilled artisans only after reading this specification. Otherembodiments may be used and derived from the disclosure, such that astructural substitution, logical substitution, or another change may bemade without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

1. An electronic device comprising: a source terminal; a heterojunctionbetween a channel layer and a barrier layer; a source electrode of ahigh electron mobility transistor overlying the channel layer; a firstresistor electrode overlying the channel layer and spaced apart from thesource electrode, wherein the first resistor electrode is coupled to thesource terminal; and a variable resistor, wherein from a top view, thevariable resistor is disposed along the heterojunction between thesource electrode and the first resistor electrode.
 2. The electronicdevice of claim 1, wherein the variable resistor has a correspondingdistance in a range from approximately 0.5 microns to 50 microns.
 3. Theelectronic device of claim 1, wherein the high electron mobilitytransistor and the variable resistor are on a same die.
 4. Theelectronic device of claim 1, wherein the variable resistor has aresistance that increases exponentially with a linear increase involtage across the variable resistor.
 5. The electronic device of claim1, further comprising a second resistor electrode that is coupled to thesource electrode.
 6. The electronic device of claim 5, furthercomprising an inductor that includes a first electrode coupled to thesource electrode and a second electrode coupled to the second resistorelectrode.
 7. The electronic device of claim 6, wherein the inductor isa planar inductor.
 8. The electronic device of claim 6, furthercomprising an interconnect that electrically connects the inductor andthe second resistor electrode to each other.
 9. The electronic device ofclaim 5, wherein the first resistor electrode includes first projectionsextending toward the second resistor electrode, and the second resistorelectrode includes second projections extending toward the firstresistor electrode.
 10. The electronic device of claim 1, furthercomprising a field electrode that overlies a portion of the variableresistor.
 11. The electronic device of claim 10, wherein the fieldelectrode is electrically connected to the first resistor electrode. 12.The electronic device of claim 10, wherein the variable resistor has acorresponding distance, and the field electrode extends over thevariable resistor in a range from 5% to 50% of the correspondingdistance.
 13. The electronic device of claim 1, further comprising agate electrode of the high electron mobility transistor and a drainelectrode of the high electron mobility transistor.
 14. The electronicdevice of claim 12, further comprising a source bond pad electricallyconnected to the first resistor electrode, and a drain bond padelectrically connecting to the drain electrode of the high electronmobility transistor.
 15. The electronic device of claim 12, furthercomprising a source plate overlying and electrically connected to thefirst resistor electrode, and a drain plate overlying and electricallyconnected to the drain electrode of the high electron mobilitytransistor.
 16. The electronic device of claim 15, wherein the sourceplate overlies a portion of the drain electrode of the high electronmobility transistor, and the drain plate overlies a portion of sourceelectrode of the high electron mobility transistor.
 17. (canceled)
 18. Acircuit comprising: a drain terminal and a source terminal; an n-channelhigh electron mobility transistor having a drain and a source, whereinthe drain is coupled to the drain terminal of the circuit; and avariable resistor having a first electrode and a second electrode,wherein: the first electrode is coupled to the source of the n-channelhigh electron mobility transistor, the second electrode is coupled tothe source terminal of the circuit, and the variable resistor has aresistance that varies as a function of at least a voltage across thevariable resistor.
 19. The circuit of claim 18, further comprising aninductor having a first electrode and a second electrode, wherein thefirst electrode of the inductor is coupled to the source of then-channel high electron mobility transistor, and the second electrode ofthe inductor is electrically connected to the first electrode of thevariable resistor.
 20. The circuit of claim 18, further comprising acontrol terminal coupled to a gate of the n-channel high electronmobility transistor.
 21. The electronic device of claim 1, wherein thehigh electron mobility transistor is an n-channel high electron mobilitytransistor.